The present invention relates generally to improvements in portable combustion-powered fastener driving tools, and specifically to improvements relating to the suspension of a motor for a combustion chamber fan for decreasing the operationally induced acceleration forces experienced by the motor, and for decreasing wear and tear on the motor.
Portable combustion-powered tools for use in driving fasteners into workpieces are described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, U.S. Pat. Nos. 4,522,162; 4,483,474; 4,403,722; 5,197,646; 5,263,439 and U.S. Pat. No. 6,520,397, all of which are incorporated herein by reference. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill.
Such tools incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine that is powered by a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in the combustion chamber provides for an efficient combustion within the chamber and facilitates scavenging, including the exhaust of combustion by-products. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a cylindrical body.
A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a workpiece contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel-metering valve to introduce a specified volume of fuel into the closed combustion chamber.
Upon the pulling of a trigger switch, which causes the ignition of a charge of gas in the combustion chamber of the engine, the piston and driver blade are shot downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original, “ready” position, through differential gas pressures within the cylinder. Fasteners are fed into the nosepiece through a magazine, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
Upon ignition of the combustible fuel/air mixture, the combustion in the chamber causes the acceleration of the piston/driver blade assembly and the penetration of the fastener into the workpiece if the fastener is present. This combined downward movement causes a reactive force or recoil of the tool body. Therefore, the fan motor, which is suspended in the tool body, is subjected to an acceleration opposite the power stroke of the piston/driver blade and fastener.
Almost immediately thereafter, a bumper at the opposite end of the cylinder stops the momentum of the piston/driver blade assembly, and the tool body is accelerated toward the workpiece. The motor and shaft are thus subjected to an acceleration force which is opposite the direction of the first acceleration. After experiencing these reciprocal accelerations, the motor oscillates with respect to the tool.
Conventional combustion powered tools require specially designed motors to withstand these reciprocal accelerations of the shaft and motor, and the resulting motor oscillations. The motors are equipped with custom modifications which result in expensive motors that increase the production cost of the tools.
Although prior suspension systems exist that are designed to stabilize the motors and prevent them from experiencing excessive acceleration forces, they are prior art systems with a larger mass or a higher level of rigidity, increasing the final manufacturing costs of the combustion-powered tools to which they pertain.
Therefore, there is a need for a motor suspension system for a combustion-powered tool with an increased resiliency that reduces operationally induced acceleration forces experienced by the tool during operation. There is also a need for a motor suspension system that accommodates the use of a more standard, cost-effective motor.